1. Field of the Invention
The present invention relates to a transport system and a method for temporarily storing articles in the transport system, and in particular relates to temporary storage of articles in the transport system that includes an overhead traveling vehicle, a local carriage, a buffer, and a load port.
2. Description of the Related Art
The inventor has proposed a transport system according to which a track for a local carriage is arranged directly below a travel rail for an overhead traveling vehicle and directly above a load port, and a buffer is arranged directly below the track for the local carriage and not in an area directly above the load port (See, for example, EP 2450297A). With this system, the local carriage transports articles to and from the load port, and therefore articles are transported to and from the load port without waiting for the overhead traveling vehicle to arrive. Also, for example, the overhead traveling vehicle transports articles to and from the buffer, and the local carriage transports articles between the buffer and the load port. JP 2011-207621A also proposes a similar system.
Another conventional technique relating to temporary storage of articles will be described next. US 2011/31091A discloses a buffer in which the cells of shelves are aligned vertically and a dolly carriage provided in an elevator is allowed to go into and out of the cells. The buffer is arranged in the vicinity of a load port and multiple articles are stored therein so that the overhead traveling vehicle may transport articles thereto and therefrom. By doing so, articles needed by a processing equipment are transported to the buffer in advance. JP 2009-62153A discloses that an elevatable rail is provided in the buffer and a carriage including a fork is allowed to travel along the rail. With this buffer, the cells of the shelves are arranged vertically, and articles are transported to and from the shelves by means of the vertical movement of the rail and the traveling of the carriage. JP 2009-62153A also discloses that the buffer is connected to the overhead traveling vehicle system and is arranged in the vicinity of the load port.
However, if the capacity of the buffer in the system disclosed in EP 2450297A is increased, the track for the local carriage increases in length. For this reason, there is a limitation to the capacity of the buffer. With regard to this point, JP 2011-207621A proposes a buffer that moves articles laterally from the overhead traveling vehicle so as to transport them. However, in order to make it possible for the local carriage to access the buffer, a mechanism for moving articles laterally to the local carriage is needed. On the other hand, the buffers disclosed in US 2011/31091A and JP 2009-62153A are not configured to be connected to a local carriage.